The Yangtze River Valley (YRV) experienced record-breaking extreme high temperature and weakened rainfall events in August 2022, which resulted in severe disasters and large socioeconomic losses. The importance of the intensification and westward movement of the western Pacific subtropical high (WPSH) with abnormal subsidence has been emphasized in previous studies. However, the source of the abnormal subsidence remains unknown. This study investigates the source of the abnormal subsidence over the YRV and discusses its possible causes by adopting the three-pattern decomposition of the atmospheric circulation (3P-DGAC). Meridional circulation (MC) was the main contributor to the abnormal vertical velocity (114%), while the contribution of zonal circulation (ZC) was negative (–14%). Additionally, the negative rainfall anomaly over the YRV can be explained mainly by the MC. The anomalous MC was characterized as a ‘negative-positive-negative-positive-negative’ quintuple distribution with sinking motion over the YRV. Anomalous MC is closely related to the sea surface temperature anomaly (SSTA) over the three oceans. The negative phase of the Indian Ocean dipole (IOD) and La Niña SSTA leads to an anomalous rising motion of the ZC over the Maritime Continent, favoring the existence of the rising motion of the MC by the coupling effect. The positive phase of the North Atlantic triple (NAT) SSTA results in an anomalous Rossby wave train, which further leads to a sinking motion over the YRV.

中文翻译：

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经向环流对2022年8月长江流域极端高温和降雨减弱的影响

2022年8月，长江流域经历了创纪录的极端高温和降雨减弱事件，造成严重灾害和重大社会经济损失。以往的研究已经强调了异常沉降的西太平洋副热带高压（WPSH）增强和西移的重要性。然而，异常沉降的来源仍然未知。本研究采用大气环流三模式分解法（3P-DGAC）探讨长江流域异常沉降的根源，并探讨其可能的成因。经向环流（MC）是垂直速度异常的主要贡献者（114%），而纬向环流（ZC）的贡献为负（–14%）。此外，长江流域的负降雨异常主要是由雨云造成的。异常MC的特征是“负-正-负-正-负”五元分布，并在长江流域上空下沉。 MC异常与三大洋海表温度异常（SSTA）密切相关。印度洋偶极子（IOD）和拉尼娜海温异常的负位相导致海洋大陆上空ZC异常上升运动，通过耦合效应有利于MC上升运动的存在。北大西洋三重海温异常 (NAT) 的正位相导致罗斯贝波列异常，进一步导致 YRV 上空下沉。